This application claims the priority of German application DE 103 08 650.1, filed 27 Feb. 2003, which is expressly incorporated by reference herein.
The invention relates to an operating method for operating an engine controller and to a corresponding engine controller.
Modern spark ignition engines generally have a three-way catalytic converter for purifying the exhaust gases. The fuel/air ratio in the exhaust gas is regulated to a value of approximately λ≈1 by means of a lambda probe arranged in the stream of exhaust gases, in order to bring about an optimum purification effect of the three-way catalytic converter for the various components of the exhaust gases.
In spark ignition engines, fuel tank venting devices are also known in which the fuel which is vaporizing in the fuel container is taken up by an activated carbon filter and buffered. This buffering of the vaporizing fuel in an activated carbon filter advantageously prevents fuel vaporizations from being able to contaminate the surrounding air. However, the absorptive capacity of such activated carbon filters is limited so that, when a predefined degree of loading is reached, the activated carbon filter is purged with fresh air and the stored fuel passes into the intake tract of the spark ignition engine and is subsequently burnt. During this purging of the activated carbon filter, the spark ignition engine changes over temporarily from the normal operating mode of a regulated lambda value into a different operating mode in which the fuel/air ratio can deviate from the setpoint value. In the known spark ignition engines, this changeover of the operating mode takes place at predefined time intervals so that the absorptive capacity of the activated carbon filter is not exceeded.
However, it is a disadvantage of this timed changeover of the operating mode that the quantity of vaporizing fuel also depends on other variables, such as, for example, the fuel temperature and fuel pressure. The timed changeover of the operating mode therefore leads to unsatisfactory results.
The invention is therefore based on the object of providing an engine controller and a corresponding operating method in which the changeover between the operating modes takes place as far as possible according to certain requirements.
The invention comprises the general technical teaching of performing the changeover of the operating mode as a function of at least one state variable of the internal combustion engine.
In one variant of the invention, the operating method according to the invention controls the switchover from the normal mode or lean mode of a spark ignition engine into a fuel tank venting mode in which an activated carbon filter is regenerated, in order to avoid exceeding the storage capacity of the activated carbon filter.
In this variant of the invention, the changeover of the operating mode can be controlled as a function of the degree of loading of the activated carbon filter. Here, the engine controller preferably changes into the fuel tank venting mode if the degree of loading of the activated carbon filter exceeds a predefined limiting value.
The degree of loading of the activated carbon filter is preferably determined by changing over into the fuel tank venting mode in a timed fashion, the activated carbon filter being purged with fresh air and as a result regenerated. The vaporizations of fuel, which are purged from the activated carbon filter, depending on the degree of loading of the activated carbon filter, cause the fuel/air mixture to be enriched, which is sensed by means of a lambda probe. The change in the fuel/air ratio during the regeneration of the activated carbon filter therefore permits the degree of loading of the activated carbon filter to be determined.
However, in this variant of the invention, pressure and/or temperature in the fuel container can also be evaluated in order to control the changeover into the fuel tank venting mode. As a result, the vaporizations of fuel in the fuel container lead not only to a rise in the degree of loading of the activated carbon filter but also to a rise in pressure in the fuel container, which permits conclusions to be drawn about the degree of loading of the activated carbon filter. The fuel temperature is also preferably evaluated as the vaporizations of fuel in the fuel container increase with the fuel temperature.
In another variant of the invention, the changeover from the normal mode or lean mode of the internal combustion engine into an operating mode in which the fuel/air ratio is adapted is controlled. In modern spark ignition engines with an exhaust gas catalytic converter, the fuel/air ratio is regulated because the purification effect of exhaust gas catalytic converters depends on the fuel/air ratio, and is also satisfactory only within a highly limited value range (referred to as the catalytic converter window) of the fuel/air ratio for the different exhaust gas components comprising hydrocarbon, nitrogen oxide and carbon monoxide. However, the regulating dynamics during the regulation of the fuel/air ratio decline in proportion to the magnitude of the error to be eliminated, with the result that the regulation of the fuel/air ratio is usually combined with a pilot control. The pilot control predefines a fuel/air ratio as a working point for the regulation of the fuel/air ratio, with the result that the regulator then only has to eliminate small errors, and therefore has good regulating dynamics. The adaptation of the fuel/air ratio has the function of setting the pilot control in such a way that, as far as possible, minimum errors are required to be eliminated at the working point of the regulator in order to achieve regulating dynamics which are as good as possible.
The changeover from the normal mode or lean mode of the internal combustion engine into the adaptation mode is preferably controlled here as a function of one or more state variables of the internal combustion engine. For example, the rotational speed of the internal combustion engine, the torque of the internal combustion engine and/or the time period since the last adaptation can be taken into account in order to control the changeover of the operating mode according to requirements.
In one preferred embodiment, an additive adaptation or a factorial or multiplicative adaptation of the fuel/air ratio is possible in the adaptation mode. The additive adaptation takes place by adding or subtracting a specific offset value to or from the working point of the pilot control system in order to optimize the working point. In contrast, in the case of factorial or multiplicative adaptation, multiplication by a specific adaptation factor is carried out in order to optimize the working point. One of these two operating modes must be selected at the changeover into the adaptation mode with the rotational speed and the torque of the internal combustion engine being preferably taken into account. A factorial adaptation is then carried out within a specific rotational speed/torque window, while an additive adaptation is carried out within another rotational speed/torque window. The changeover into the factorial adaptation mode or into the additive adaptation mode is therefore controlled as a function of the rotational speed and the torque of the internal combustion engine.
The factorial adaptation is preferably carried out if the torque and the rotational speed exceed predefined eliminating values, while the additive adaptation is carried out if the torque and the rotational speed drop below predefined limiting values.
The invention is not restricted to controlling a spark ignition engine but rather can also be applied in a diesel engine which has various operating modes.
Other advantageous developments of the invention are contained in the subclaims or are explained below together with the description of the preferred exemplary embodiment of the invention with reference to the drawings, in which: